The Application is generally directed to a novel method for image processing of printed dots on spherical objects and, more specifically, diffusely-reflective dots, such as painted dots, on golf balls.
Apparatus for measuring the flight characteristics of spherical objects, such as golf balls, are known in the art. Methods for detecting golf club head position and golf ball position shortly after impact using photoelectric means to trigger a flash to permit a photograph to be taken of the club head have been disclosed in U.S. Pat. Nos. 4,063,259; 4,158,853, and 4,375,887, which are incorporated in their entirety herein by reference. Golf ball or golf club head movement has been determined by placing reflective areas on a golf ball and determining their position with electro-optical sensors, such as disclosed in U.S. Pat. No. 4,136,387. The use of electro-optical sensing of light sources, on both a golfer""s body and a golf club, and apparatus for monitoring a golfer and a swinging golf club has been disclosed in U.S. Pat. No. 4,137,566.
One troublesome aspect of the most successful systems currently in use for measuring golf ball flight characteristics is the required use of strobe illumination of reflective dots adhered to specific locations on a golf ball. Examples of such systems are disclosed in U.S. Pat. Nos. 5,471,383; 5,501,463; 5,575,719; and 5,803,823, which are incorporated in their entirety herein by reference. These systems generally require cameras, sensors, and strobe lights positioned to illuminate the golf ball, and thus the reflective dots, at two different times immediately after impact with a golf club. The images of the reflective dots are subsequently analyzedxe2x80x94from the changes in the relative positions of the reflected images, as a function of time, a number of golf ball flight characteristics, such as ball velocity, launch angle, side angle, and spin rate, may be calculated. While the illumination of reflective dots has proved to be a successful method for attaining ball flight characteristics, in many cases this method does not provide a true measure of the actual ball flight characteristics. Adhering reflective dots to the surface of a golf ball can affect the ball flight characteristics in a negative way. The reflective dots are usually thick, thereby providing raised protrusions on the ball surface. As such, the raised dots impart asymmetry to the lift and drag and differing backspin and sidespin are imparted on the ball, all of which affect ball trajectory and, therefore, distance. Further, it is difficult to repeatably attach the reflective dots in precise locations, as they are attached adhesively onto a dimpled surface.
One area that has not been adequately addressed by past golf ball launch monitoring systems relates to the image processing of diffuse markings, such as paint or ink dots on golf balls, to obtain golf ball flight characteristics. Paint or ink dots may be applied thin enough that no measurable distortion in trajectory is observed. While replacing reflective tape dots with ink dots eliminates the aforementioned flight characteristic problems, analyzing gray-scale images of golf balls in order to obtain the locations of paint dots on a golf ball presents a unique image processing problem, especially when the ball is in flight and multiple strobe flashes are used. Therefore, it would be useful to develop a method in which one could automatically identify, and determine the position of, diffuse paint from an optical image in a straightforward manner without significant input from the user or golfer.
The present invention is directed to a method of automatically calculating the spatial relationship of a plurality of diffuse dots on a ball, comprising the automated steps of obtaining at least two ball images of the ball at two or more discrete times; calculating a first gray level of the image; smoothing and binarizing the image; locating and determining the number of ball images in the image; locating and determining the number of painted dots on each ball image; confirming that the calculated number of dots equals a predetermined number of dots on each ball image; and calculating movement characteristics of the ball.
In one embodiment, the first gray level is calculated using an iterative selection algorithm. Preferably, the step of locating and determining the number of ball images in the image further comprises determining a boundary of the ball images in the image and calculating a region of interest around each boundary. Additionally, the step of determining the boundary of the balls in the image further comprises a contour following or a boundary chain algorithm. Preferably, the region of interest is rectangular.
In another embodiment, the step of locating and determining the number of diffuse dots on each ball images further comprises the steps of isolating the region of interest; inverting the image; and calculating a second gray level to provide a threshold value. In still another embodiment, the step of determining the number of diffuse dots on each ball image further comprises the steps of identifying at least one discrete object within the image using a contour tracing or a boundary chain algorithm; calculating an area, a centroid, and an aspect ratio for each discrete object in the region of interest; and filtering the objects based on the area and aspect ratio.
The step of determining a gray level the calculated number of dots equals the predetermined number of dots on each ball image preferably further comprises using a Golden Mean algorithm. In one embodiment, the characteristics of the ball comprise magnitude of velocity, direction of velocity, magnitude of spin, direction of spin. In another embodiment, the direction of velocity is defined as angles relative to an orthogonal gravity oriented coordinate system. In yet another embodiment, the direction of spin is defined as components of spin about an orthogonal axis system.
The dots should have a thickness of less than about 0.001 inches and are, preferably, pad printed or inkjet printed on the ball.